Elasto-plastic analysis of stresses in intersecting cylindrical shells strengthened by an overlay ring

Abstract

The problem of the elasto-plastic analysis of a vessel with a branch pipe reinforced by a overlay ring is examined. An applied procedure developed for analysis of intersecting shells with use of the finite-element method, theory of shells, and theory of plastic flow is employed to solve the problem. Results are presented for comparison of computed and experimental data on the model of a vessel with a radial branch pipe under internal pressure. Various means are examined for approximation of the actual deformation diagram of the material, and their effect on maximum stresses in shells subject to elasto-plastic deformation. Results are presented for the limiting plastic pressure in a vessel with a branch pipe calculated using the criterion of a double elastic gradient.Structural connections in the form of intersecting cylindrical shells have come into widespread use in various technical entities. Branch or connecting pipes on the cylindrical housings of vessels operating under an excess internal pressure are typical examples of these connections. Internal excess pressure is the basic load for which the geometric parameters of vessels are determined.It is well known [1] that a local induced stress state, which is characterized by high stress concentration, especially for thin-wall shells, develops in the region of shell intersection. Different methods of local reinforcement of vessels at the point of connection with a branch pipe are used to reduce the level of maximum stresses. Here, selection of the means of reinforcement should be substantiated with consideration of both its effect on maximum stresses in the shells, and also structuralprocedural limitations. Reinforcement by an overlay ring is one of the simplest and most effective means of local attachment of vessels to branch pipes, proceeding from structural design and production realization. This paper presents results of an investigation of the elasto-plastic strains and stresses that develop when the housing of a vessel is attached to a branch pipe in the connection zone, as determined by the finite-element method (FEM).The connection has two planes of symmetry: a principal plane passing through the axis of both shells -the basic shell and the shell of the branch pipe; and a transverse plane passing through the axis of the of the branch pipe and perpendicular to the principal plane. The stress state of the reinforced connection between the intersecting shells under consideration will depend on the following set of basic relative geometric parameters:where d/D is the ratio of the diameters of the median surfaces of the branch pipe and basic shell, D/H is a parameter of the thinness of the wall of the basic shell, h/H is the ratio of the thickness of the branch pipe to that of the basic shell, and H o /H is the relative thickness of the overlay ring.

Limiting plastic load for a pressure vessel with a tangential branch pipe

“…The elasto-plastic deformation of such a connection is investigated by the finite-element method (FEM) using two-dimensional shell elements, and the theory of plastic flow with isotropic hardening. The specialized computer program SAIS, some results of the testing of which are presented in [3][4][5], has been developed for elasto-plastic analysis of connections between intersecting shells.For tangential connections subject to elastic analysis, the maximum stresses in the shell will depend on the following set of relative parameters: …”